The present invention relates to polymerizable organic compositions and polymerizates having a refractive index of at least 1.57 and an Abbe number of at least 33, which are prepared from such compositions. More particularly, the present invention relates to certain polymerizable organic compositions comprising a mixture of thio(meth)acrylate functional monomers, an aromatic monomer having at least two vinyl groups, a polythiol monomer having at least two thiol groups, and a comonomer selected from an anhydride monomer having at least one ethylenically unsaturated group and/or a monomer having at least three (meth)acryloyl groups.
Polymeric materials, such as plastics, have been developed as alternatives and replacements for silica based inorganic glass in applications such as, optical lenses, fiber optics, windows and automotive, nautical and aviation transparencies. These polymeric materials can provide advantages relative to glass, including, shatter resistance, lighter weight for a given application, ease of molding and ease of dying. Representative examples of such polymeric materials include, poly(methyl methacrylate), polycarbonate and poly(diethylene glycol bis(allylcarbonate)).
The refractive indices of many polymeric materials are generally lower than that of high index glass. For example, the refractive index of poly(diethylene glycol bis(allylcarbonate)) is about 1.50, compared to that of high index glass, which can range, for example, from 1.60 to 1.80. When fabricating lenses to correct a given degree of visual defect, e.g., a correction for myopia, the use of a polymeric material having a lower refractive index will require a thicker lens relative to a material having a higher refractive index, e.g., high index glass. If the degree of correction required is substantial, e.g., in the case of severe myopia, a lens fabricated from a low index polymeric material can become so thick as to negate any benefit of reduction in weight relative to an equivalent degree of correction obtained from a higher refractive index lens, e.g., a high index glass lens. In addition, thicker optical lenses are not aesthetically desirable.
Polymeric materials prepared from the polymerization of monomers containing aromatic rings typically have high refractive indices. However, articles, such as optical lenses, prepared from such high index polymeric materials generally have lower Abbe numbers (also known as nu-values). Lower Abbe numbers are indicative of an increasing level of chromatic dispersion, which is typically manifested as an optical distortion at or near the rim of the lens.
More recently, polymeric materials having a combination of high refractive indices, e.g., of at least 1.57, and low levels of chromatic dispersion, e.g., having Abbe numbers of at least 33, have been prepared from monomers containing sulfur atoms. While possessing a desirable combination of high refractive indices and Abbe numbers, such sulfur atom containing polymeric materials often have physical properties, e.g., heat and impact resistance, that are in some instances less than desirable. For example, the impact resistance of an optical lens is a particularly important safety related physical property, and improvements in impact resistance of optical lenses prepared from sulfur-containing polymeric materials are accordingly desirable.
There is, therefore, a need for the continued development of transparent polymerizates, in particular optical lenses, that possess a combination of high refractive index and adequately high Abbe numbers, e.g., preferably at least 33 and more preferably at least 35. It is further desirable that these polymeric materials also possess improved physical properties, such as thermal properties and impact resistance.
U.S. Pat. No. 5,917,006 describes a polymerizable organic composition comprising an aromatic monomer having at least two vinyl groups, e.g., divinyl benzene, a polythiol monomer having at least two thiol groups, e.g., pentaerythritol tetrakis(2-mercaptoacetate), and an anhydride monomer having at least one ethylenically unsaturated group, e.g., methacrylic anhydride. The ""006 patent does not describe compositions comprising thioacrylate and/or thiomethacrylate functional monomers.
U.S. patent application Ser. No. 09/037,108, filed Mar. 9, 1998 (now U.S. Pat. No. 5,976,422) describes a polymerizable organic composition comprising at least one polymerizable monomer having at least two ethylenically unsaturated groups, e.g., divinyl benzene, a novel polythiol monomer, e.g., thioglycerol bis(2-mercaptoacetate), and optionally a monoethylenically unsaturated monomer, e.g., phenoxyethyl methacrylate, and/or an anhydride monomer, e.g., methacrylic anhydride. The compositions of the ""108 application are not described as comprising thioacrylate and/or thiomethacrylate functional monomers.
U.S. Pat. No. 5,384,379 describes sulfur-containing polymethacrylates produced by the radical polymerization of the unrefined products resulting from the synthesis of a thio(meth)acrylic acid ester monomer. The ""379 patent describes the radical polymerization of a monomer component having two thio(meth)acrylic acid ester groups and a chain extended monomer component having two thio(meth)acrylic acid ester groups.
U.S. Pat. No. 5,422,422 describes a high refractive index plastic produced by the reaction of an alkylthiol containing at least two thiol groups, and an alkylpolythiol ester, which contains at least two thiol groups esterified with (meth)acrylic acid. U.S. Pat. No. 4,931,521 describes a process for producing a high refractive index optical material from the radical polymerization of at least one polyfunctional thioacrylate or polyfunctional thiomethacrylate and optionally at least one other radically polymerizable monomer.
In accordance with the present invention, there is provided a polymerizable composition comprising:
(a) a mixture of thio(meth)acrylate functional monomers comprising,
(i) a first thio(meth)acrylate functional monomer represented by the following general formula I, 
xe2x80x83in which R1 is hydrogen or methyl, and Q is a divalent linking group selected from linear or branched C2-C12 alkylene, C4-C12 cyclic alkylene, C6-C14 arylene and C7-C26 alkarylene, the carbon chains of Q may optionally contain at least one linkage selected from the group consisting of ether, thioether and combinations thereof; and
(ii) a second thio(meth)acrylate functional monomer represented by the following general formula II, 
xe2x80x83in which R1 and Q have the same meanings as described for monomer (a)(i), and u is an integer from 1 to 10, e.g., u may be an integer selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and combinations thereof;
(b) an aromatic monomer having at least two vinyl groups;
(c) a polythiol monomer having at least two thiol groups; and
(d) a comonomer selected from,
(i) an anhydride monomer having at least one ethylenically unsaturated group;
(ii) a monomer having at least three (meth)acryloyl groups represented by the following general formula III, 
xe2x80x83in which R12 is a polyvalent radical of a polyol, R13 is hydrogen or methyl, and k is a whole number from 3 to 6; and
(iii) mixtures of monomers (d)(i) and (d)(ii), wherein the amount of each monomer and comonomer are selected such that a polymerizate of said polymerizable composition has a refractive index of at least 1.57, as determined in accordance with American Standard Test Method (ASTM) number D542-95, and an Abbe number of at least 33, as determined using an appropriate instrument, e.g., a Bausch and Lomb ABBE-3L Refractometer.
Other than in the operating examples, or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, etc. used in the specification and claims are to be understood as modified in all instances by the term xe2x80x9cabout.xe2x80x9d
Polymerizable compositions-according to the present invention comprise a mixture of thio(meth)acrylate functional monomers (a)(i) and (a)(ii) as described above. The mixture of thio(meth)acrylate functional monomers preferably contains a minor amount of the first thio(meth)acrylate functional monomer (a)(i) and a major amount of the second thio(meth)acrylate functional monomer (a)(ii). The first thio(meth)acrylate functional monomer (a)(i) is typically present in an amount of from 5 percent by weight to 49 percent by weight, preferably from 10 percent by weight to 45 percent by weight, and more preferably from 20 percent by weight to 40 percent by weight, based on the total weight of the mixture of thio(meth)acrylate functional monomers (a). The second thio(meth)acrylate functional monomer (a)(ii) is typically present in an amount of from 51 percent by weight to 95 percent by weight, preferably from 55 percent by weight to 90 percent by weight, and more preferably from 60 percent by weight to 80 percent by weight, based on the total weight of the mixture of thio(meth)acrylate functional monomers (a).
The weight ratio of the first thio(meth)acrylate functional monomer (a)(i) to the second thio(meth)acrylate functional monomer (a)(ii) in the polymerizable composition of the present invention is typically from 0.1:1.0 to 0.6:1.0, and preferably from 0.2:1.0 or 0.3:1.0 to 0.5:1.0. The relative amounts of the first and second thio(meth)acrylate functional monomers (a)(i) and (a)(ii) present in the composition may vary as described, and are typically selected such that the physical properties (e.g., refractive index, Abbe number, thermal properties, and in particular impact resistance) of a polymerizate prepared from the polymerizable composition are optimized.
The relative amounts of thio(meth)acrylate functional monomers (a)(i) and (a)(ii) present in the mixture of thio(meth)acrylate functional monomers (a) may be determined by methods known to the skilled artisan. Typically, this determination is accomplished by a comparison of the peak areas resulting from gel permeation chromatography (GPC) analysis of the mixture of thio(meth)acrylate functional monomers using polystyrene standards. As used herein and in the claims, the term xe2x80x9c(meth)acrylatexe2x80x9d and similar terms, e.g., xe2x80x9c(meth)acryloyl,xe2x80x9d refers to methacrylates, acrylates and mixtures of methacrylates and acrylates.
With reference to general formulas I and II, examples of linear or branched C2-C12 alkylenes from which Q may be selected, include, but are not limited to, 1,2-ethylene, propylene (e.g., 1,3-propylene and 1,2-propylene), butylene (e.g., 1,4-butylene and 1,2-butylene), pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene and dodecylene. Preferred C2-C12 alkylenes from which Q may be selected include 1,2-ethylene, 1,3-propylene and mixtures thereof. Examples of C4-C12 cyclic alkylenes from which Q may be selected, include, but are not limited to, cyclobutylene (e.g., 1,3-cyclobutylene), cyclopentylene (e.g., 1,2-cyclopentylene), cyclohexylene (e.g., 1,2-cyclohexylene), cycloheptylene, cycloctylene, cyclononylene, cyclodecylene, cycloundecylene and cyclododecylene (e.g., 1,1-cyclododecylene). Examples of C6-C14 arylenes from which Q may be selected, include, but are not limited to, phenylene (e.g., 1,2-phenylene and 1,3-phenylene), naphthalenylene (e.g., 1,4-, 1,5-, 2,6- and 2,7-naphthalenylene), and anthracenylene (e.g., 1,3- and 9,10-anthracenylene). Examples of C7-C26 alkarylenes from which Q may be selected, include, but are not limited to, toluenylene (e.g., 3,4-toluenylene), and bis(phenylene)alkane (e.g., bis(phenylene)methane, 1,2-bis(phenylene)ethane, 2,2-bis(phenylene)propane and 1,3-bis(phenylene)propane).
With further reference to general formulas I and II, the divalent linking group Q is a residue of the polythiol or salt of the polythiol used in the synthesis of the mixture of monomers (a)(i) and (a)(ii). Examples of polythiols (and the corresponding salts derived from such polythiols) that may be used to synthesize the mixture of thio(meth)acrylate monomers of the composition of the present invention, include, but are not limited to, 1,2-ethanedithiol (1,2-ethylenedithiol), 2,2xe2x80x2-thiodiethanethiol, 1,3-propanedithiol, 1,4-butanedithiol, 2,3-butanedithiol, 1,5-pentanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, 1,9-nonanedithiol, 1,3-cyclobutanedithiol, 1,1-cyclobutanedithiol, 1,2-cyclopentanedithiol, 1,2-cyclohexanedithiol, 1,2-benzenedithiol, 1,3-benzenedithiol, 1,4-naphthalenedithiol, 1,5-naphthalenedithiol, 2,6-naphthalenedithiol, 2,7-naphthalenedithiol, 1,3-antracenedithiol, 9,10-antracenedithiol, 3,4-toluenedithiol, 4,5-dimethyl-o-xylene-xcex1,xcex1xe2x80x2-dithiol, bis(phenylthiol)methane, 1,3-bis(pheneylthio)propane and 2,2-bis(phenylthio)propane. Preferably, the polythiol(s) is selected from linear or branched C2-C12 alkanedithiols, e.g., 1,2-ethanedithiol and 1,3-propanedithiol.
The thio(meth)acrylate functional monomers (a)(i) and (a)(ii) may be prepared separately and then mixed together, or more preferably they are prepared concurrently within the same reaction vessel. The mixture of thio(meth)acrylate functional monomers is typically prepared, as is known to the skilled artisan, from the reaction of: (A) a polythiol, e.g., 1,2-ethanedithiol, or a salt of a polythiol, e.g., 1,2-ethanedithiol disodium salt; with (B) a (meth)acryloyl halide, e.g., (meth)acryloyl chloride, or (meth)acrylic anhydride. The relative amounts of monomers (a)(i) and (a)(ii) resulting from this reaction can be controlled by selecting the molar ratio of reactants (B) to (A). In the case when reactant (B) is (meth)acrylic anhydride, the molar ratio of reactants (B) to (A) is typically from 1.3:1 to 2.5:1, e.g., from 1.5:1 to 2.0:1.
A more detailed general method of preparing mixtures of thio(meth)acrylate monomers useful in the compositions of the present invention, in which Q is 1,2-ethylene and R1 is methyl (with reference to general formulas I and II) is as follows. An aqueous solution containing approximately 18 percent by weight of 1,2-ethylenedithiol disodium salt (e.g., 336.2 parts by weight) is added slowly to a suitable reaction vessel containing methacrylic anhydride (e.g., 100 parts by weight) and a suitable solvent (e.g., 418.2 parts by weight of methylene chloride). The contents of the reaction vessel are mixed under a nitrogen sweep and at a temperature of from 15xc2x0 C. to 30xc2x0 C. during the salt addition. After completion of the 1,2-ethylenedithiol disodium salt addition, the contents of the reaction vessel are typically mixed for an additional 2 hours at a temperature of from 20xc2x0 C. to 30xc2x0 C. under nitrogen sweep. A post-addition of a small amount of methacrylic anhydride (e.g., 2.5 parts by weight) is made to the reaction vessel, followed by the addition of an aqueous solution containing 13 percent by weight of calcium chloride hexahydrate (e.g., 170 parts by weight). The contents of the reaction vessel are then stirred for at least 15 minutes under air.
Work-up of the contents of the reaction vessel typically involves separating out the organic phase, and adding to it a radical polymerization inhibitor (e.g., 0.0075 parts by weight of para-methoxy phenol). The organic phase is washed with an aqueous solution (e.g., 400 parts by weight of an aqueous solution containing 5 percent by weight calcium chloride hexahydrate), followed by removal of organic solvent by vacuum distillation. The product resulting from the described general synthetic method is a mixture of thiomethacrylate monomers comprising a minor amount of the first thiomethacrylate functional monomer (a)(i) (e.g., 35 percent by weight of monomer (a)(i), based on the total weight of monomers (a)(i) and (a)(ii)), and a major amount of at least one chain extended second thiomethacrylate functional monomer (a)(ii) for which u is an integer from 1 to 10 (e.g., 65 percent by weight of monomer (a)(ii), based on the total weight of monomers (a)(i) and (a)(ii)).
The mixture of thio(meth)acrylate functional monomers (a) are typically present in the composition of the present invention in an amount of at least 20 percent by weight, preferably at least 30 percent by weight, and more preferably at least 40 percent by weight, based on the total monomer weight of the polymerizable composition. Also, the mixture of thio(meth)acrylate functional monomers is typically present in the composition in an amount of less than 80 percent by weight, preferably less than 70 percent by weight, and more preferably less than 60 percent by weight, based on the total monomer weight of the polymerizable composition. The mixture of thio(meth)acrylate functional monomers (a) may be present in the polymerizable composition in an amount ranging between any combination of these values, inclusive of the recited values.
The composition of the present invention also comprises an aromatic monomer having at least two vinyl groups. Examples of aromatic monomers include, but are not limited to: divinyl benzene, e.g., 1,2-divinyl benzene, 1,3-divinyl benzene, 1,4-divinyl benzene and mixtures of structural isomers of divinyl benzene; diisopropenyl benzene, e.g., 1,2-diisopropenyl benzene, 1,3-diisopropenyl benzene, 1,4-diisopropenyl benzene and mixtures of structural isomers of diisopropenyl benzene; trivinyl benzene, e.g., 1,2,4-triethenyl benzene, 1,3,5-triethenyl benzene and mixtures of structural isomers of trivinyl benzene; divinyl naphthalene, e.g., 2,6-diethenyl naphthalene, 1,7-diethenyl naphthalene, 1,4-diethenyl naphthalene and mixtures of structural isomers of divinyl naphthalene; halogen substituted derivatives of divinyl benzene, diisopropenyl benzene, trivinyl benzene and divinyl naphthalene, e.g., 2-chloro-1,4-diethyenyl benzene; and mixtures of such aromatic monomers. In a particularly preferred embodiment of the present invention, the aromatic monomer is divinyl benzene.
The aromatic monomer having at least two vinyl groups is typically present in the polymerizable composition of the present invention in an amount of at least 5 percent by weight, preferably at least 10 percent by weight, and more preferably at least 15 percent by weight, based on the total monomer weight of the polymerizable composition. The aromatic monomer is also typically present in an amount of less than 65 percent by weight, preferably less than 47 percent by weight, and more preferably less than 30 percent by weight, based on the total monomer weight of the polymerizable composition. The aromatic monomer may be present in the polymerizable composition in an amount ranging between any combination of these values, inclusive of the recited values.
Also present in the compositions of the present invention is a polythiol monomer having at least two thiol groups. By xe2x80x9cthiol groupxe2x80x9d is meant an xe2x80x94SH group which is capable of forming a covalent bond with an ethylenically unsaturated group, e.g., a vinyl group. As used herein and in the claims, the prefix xe2x80x9cthioxe2x80x9d (as in xe2x80x9cthio(meth)acrylate functional monomerxe2x80x9d), refers to a divalent sulfur atom (i.e., xe2x80x94Sxe2x80x94) that is not covalently bonded to a hydrogen atom. The term xe2x80x9cthiol groupxe2x80x9d and the prefix xe2x80x9cthioxe2x80x9d are accordingly distinguishable from each other in the present specification. Not intending to be bound by any theory, it is believed that covalent bonds are formed between the thiol groups and ethylenically unsaturated groups of the monomers of the present invention by means of a thiolene reaction mechanism, as it is known to those of ordinary skill in the art.